1. Technical Field of the Invention
The invention concerns a tire with a semi-radial or radial carcass reinforcement, the tire being intended more particularly for fitting on vehicles that can roll at high speeds.
2. The Related Art
In the tire considered, the carcass reinforcement, whose reinforcing elements are inclined relative to the circumferential direction at angles between 80xc2x0 and 90xc2x0, the reinforcement then being termed radial, or whose reinforcing elements are inclined relative to the circumferential direction at angles between 60xc2x0 and 80xc2x0, the reinforcement then being termed semi-radial, is anchored in each bead to an anchoring wire or bead wire. The carcass reinforcement is covered radially by a crown reinforcement formed of at least two plies of reinforcing elements parallel to one another in each ply and crossed from one ply to the next, which make angles of small value relative to the circumferential direction. The crossed crown plies are generally completed radially on the outside by at least one ply of circumferential textile cables.
The sidewalls of the tire, containing radial or semi-radial reinforcing elements, are structurally the most flexible parts of the tire, since the elements have a strength that is generally calculated simply to withstand the tensile stresses imposed by the inflation pressure. In the case of the tires considered, moreover, the reinforcing elements are textile elements in by far the majority of cases, and are therefore quite incapable on their own of resisting compression stresses.
In the case of radial tires required to work at high speeds, problems arise when vehicles accelerate or brake abruptly, because the torque, which increases or decreases very rapidly, cannot be transferred directly to the tread of the tire which is in contact with the ground. For example, during a sudden acceleration the engine torque is transmitted from the wheel hub to the tire tread via the reinforcing elements of the carcass reinforcement. The resistance offered by the carcass reinforcement is insufficient and the reinforcing elements are subjected to deformations which cause the tire bead to rotate on the mounting rim of the tire without any torque transmission. A similar phenomenon arises in the case of emergency braking at high speed.
Various possibilities have been explored in the attempt to reduce the notorious insufficiency in relation to the above problems of the known radial tires: a first attempt was to reduce the ratio of the height of the tire to its maximum axial width; a second consisted in having a carcass reinforcement strengthened in the sensitive area of the tire sidewalls by the addition of supplementary reinforcements of crossed elements. The multiplication of additional reinforcement armatures in the sidewalls only partially solves the problems that arise, since the number and thickness of such reinforcements are limited in particular by the increase in weight, increases in the operating temperature, and the reduction of the rolling comfort to which they give rise.
To confer upon a tire, more particularly one with a radial carcass reinforcement, greater stability during rolling but without adverse effect upon comfort, U.S. Pat. No. 2,186,178 proposes to arrange at the junction between the bead and the sidewall of the tire an additional or secondary bead wire. The carcass reinforcement and additional reinforcement armatures are such that the two bead wires serve to anchor the reinforcements.
Patent FR 1 590 025, which is the equivalent of U.S. Pat. No. 3,631,913, adopts essentially the same principle, which it improves by adding an adapted carcass reinforcement section in the sidewall of the tire. When the tire is mounted on its operating rim and inflated to the recommended pressure, the portion of the carcass reinforcement adjacent to the tread extends as far as beyond the half-height of the sidewall, such that its distance from the median plane increases progressively and its meridian profile curves inwards relatively little, while the second portion interposed radially between the first portion and the bead wire that anchors the carcass reinforcement has a smaller radial height and a meridian profile with a relatively very marked inward curvature, the two portions described being joined by a second circumferential reinforcement in the form of a bead wire. The same principle of an additional bead wire located at the junction of the sidewall and the tire bead is also adopted by patent DE 2 357 265.
To preserve the well known advantages conferred by a high overall rigidity of the crown reinforcement of a radial tire and to produce high-performance tires, the present invention proposes a solution in which the transverse and longitudinal rigidities of at least one sidewall are increased, based on the principle of an additional reinforcement ring in at least one sidewall.
The tire according to the invention comprises a tread, two beads, and two sidewalls radially interconnecting the tread and the beads, each bead having at least one annular anchoring element, a carcass reinforcement comprising at least one ply of reinforcing elements parallel to one another within the ply and making with the circumferential direction an angle xcex1 such that 60xc2x0xe2x89xa6xcex1xe2x89xa690xc2x0, the at least one ply being anchored in each tire bead to at least one annular anchoring element, a crown reinforcement radially surmounting the carcass reinforcement, and an inextensible reinforcement ring in at least one of the sidewalls, wherein, when the tire is viewed in meridian section fitted on its operating rim and inflated to the recommended pressure, the inextensible reinforcement ring is located axially inside the at least one carcass reinforcement ply, and a profiled element of rubber mixture is positioned radially between the annular anchoring element in the bead of the at least one of the sidewalls and the inextensible reinforcement ring, and is located axially inside the ply.
xe2x80x9cAnnular anchoring element in the beadxe2x80x9d means any element that absorbs the tensile stresses in the carcass reinforcement produced by the inflation pressure. As is known in its own right, the element can be a bead wire, generally formed of circumferential cords or cables, or more generally a stack of several strips of cords or cables, which make with the circumferential direction an angle of zero or at most 10xc2x0. As is known, anchoring is effected by adhesion over a sufficient length of the carcass reinforcement to the annular element, and the adhesion surface can be of semi-toroidal shape (as is the case when the carcass reinforcement is wrapped around a covered bead wire), or it can be a cylindrical or frustoconical surface or a surface in the shape of a circular crown (as is the case when a carcass reinforcement is adhesively bonded to or inserted between one (or more) strip(s) of circumferential or quasi-circumferential cords or cables).
The inextensible reinforcement ring is preferably located radially a distance H2 away from the base of the bead which is larger than one-third of the height H of the tire on its rim, which enables the meridian profile of the carcass reinforcement to be modified, particularly in the shoulder area of the tire.
The inextensible reinforcement ring can take several forms: it can be a monofilament with more or less large cross-section dimensions; it can be in the form of a braided assembly, whether this be a bead wire or an actual cable; or it can be in the form of a stack of circumferential cords or cables and the stack can be parallel to the equatorial plane or parallel to a radial plane.
In an equivalent way, the additional ring can be made of a single material having an appropriate tensile rigidity in all cases greater than the average rigidity of rubber mixtures. In particular, the additional ring may be made of a plastic material, polyurethane, aromatic polyamide, resin reinforced with various fibers (carbon, glass, etc.), or even of metal. The additional ring can also comprise two or more materials.
The additional ring can be hollow, to reduce the weight.
In an also equivalent manner, the additional sidewall ring and the profiled element of rubber mixture can be integrated in a single element, which can for example be produced independently of the fabrication of the tire itself and can then be incorporated in the tire at the time of its fabrication.
This single element can be made of a single material or of a composite material (i.e. a material comprising a matrix strengthened by reinforcements so as to confer upon the element the appropriate rigidities). When the single element is used instead of an additional ring and a profiled element of rubber mixture, its cross-section will be appropriate to obtain the rigidity desired and hence the mechanical effect sought in the tire. Of course, to obtain a good bond between the single element and the rubber mixtures of the tire, the surface of the element can be treated to improve adhesion. Orifices can also be made through the element to allow the passage of the rubber mixtures of the tire during its molding and vulcanization.
An essential feature of the invention is the mechanical coupling produced between the additional sidewall ring and the tire bead, by means of the profiled element of rubber mixture which extends the ring radially inwards.
To derive maximum benefit from this mechanical coupling effect, the profiled element of rubber mixture axially inside the axially outer carcass ply has a Shore A hardness at least equal to 65, so that its resistance to compression stresses is good.
The transverse rigidity of the tire is a function of the inclination of the line segment joining the centers of gravity of the meridian sections of the bead anchoring elements and the additional sidewall ring. It is advantageous for the line segment to make an angle xcfx86 with the axial direction, which is open radially and axially towards the outside and is at most equal to 70xc2x0.
To increase the efficacy of force and torque transmission, the carcass reinforcement comprises at least two plies of reinforcing elements parallel to one another in each ply and making an angle between 60xc2x0 and 90xc2x0 with the circumferential direction, at least one of the plies being anchored in each bead by wrapping around the anchoring element, and the second ply, called the axially inner ply, being located axially inside the additional sidewall ring and profiled element of rubber, between the additional ring and the anchoring element in the bead.
It is advantageous for the carcass reinforcement to have three carcass plies:
the axially outer ply, which is preferably discontinuous and is composed of two half-plies of radial, textile reinforcing elements parallel to one another in each half-ply and making with the circumferential direction an angle that can be between 80xc2x0 and 90xc2x0, each half-ply having, on the one hand, a radially upper end under the edge of the crown reinforcement and, on the other hand, a radially lower edge with its end at the level of the anchoring element in the bead, and being arranged axially outside the profiled element between the anchoring element and the sidewall ring, outside the sidewall ring and on the outside, in the upper sidewall,
two main carcass plies, axially on the inside, formed of textile reinforcing elements crossed from one ply to the next so as to make with the circumferential direction angles of between 60xc2x0 and 80xc2x0, and being wrapped within each bead around the anchoring element to form upturns axially outside the edge of the axially outer carcass ply.
Preferably, the carcass reinforcement plies are formed of textile reinforcing elements such as aliphatic or aromatic polyamide, polyester, or rayon, which are parallel to one another in each ply.
The structure of each bead can be completed by at least one additional reinforcement armature. This is composed of at least one ply of textile and/or metallic elements which make with the circumferential direction an angle between 0xc2x0 and 45xc2x0, such ply being arranged either outside or inside the main plies of the carcass reinforcement, inside or outside the axially outer ply.
The thickness of the rubber profiled element between the main carcass reinforcement and the additional ply, measured perpendicularly to the line joining the centers of gravity of the anchoring element and the additional ring, is a minimum essentially at the level of the element and ring, and maximum approximately towards the geometrical middle of the profiled element. Viewed in cross-section, the rubber profiled element has an elongated and almost rectilinear or substantially rectilinear shape, and its maximum thickness is at least equal to 3% of the height of the tire on its rim.